U.S. Pat. No. 3,827,086 discloses a tub-shower. FIG. 6 shows a joint between the backwall panel and a sidewall panel. The joint is described at Col. 5, lines 12--31. There is a channel 54 for caulking and there are holes 55 for screw fasteners. Many times the screw fasteners did not hold and leakage could occur through the joint.
U.S. Pat. No. 4,180,874 refers at Col. 8, lines 44-47, to "metal clips or latches" for securing the panels together. These latches were similar to those on metal toolboxes. The provision for the securing of the two latch parts of each latch respectively to the two panels was expensive, involving thickened molded portions on the panels for the reception of threaded metal inserts. Many times an installer did not attach the latch parts by threading screws into the metal inserts, and leakage through the joint could occur.